Hi all,

Following standard methods, I am separating alky sodium sulfonates on a RP column with a mixture of methanol and aqueous sodium perchlorate as eluent, and RI detection.

It works fine, but I'm still wondering what the mechanism is. That is, is sodium perchlorate the key, or is it just ionic strength, or am I missing something obvious?

Thanks for your answers...

Must be just ionic strength. Anything happening when you increase or reduce the concentration?

how can I caracterize the sodium tripolyphosphate?

I have two methods for separating alkylbenzene sulfonates on an octyl{C-8} RP column. Both are gradient. One uses methanol water and the other acetonitrile water. My detector is UV because of the benzene ring. I have used this method for both the salts and acids. You cannot use gradient with an RI detector. You might want to try a general UV wavelength that detects everything but your mobile phase solvents and try gradient elution. As for the salt. I think it is just there as a buffering conditioner to protect the column. Separation is reverse phase by interaction between the analytes homologus alkyl groups and the stationary phase.

Incidently, I was browsing through a Dionex catalogue yesterday and came across the exact separation you are doing. It was done by Capilary Electrophoreseis, which I have probably spelled wrong. Get a hold of their catalogue, contact them by telephone or internet. Their website is WWW.DIONEX.COM.

For further details contact me at HJAMIESON99@HOME.COM.